Field of the Invention
The present invention is directed to a container and to a method for manufacturing from thermoplastic material a hollow container having an integral lifting handle.
In fabricating large hollow bodies, such as, for example, 55 gallon drums, from thermoplastic materials, it is common practice to blow-mold such bodies from an extruded, hollow, tubular shaped preform or parison. The parison is placed within an open blow-mold apparatus, the apparatus is closed and air blown into the parison to force it to expand outward against walls of the mold apparatus. Generally, it is desirable to provide lifting handles or roller chimes about the formed body for ease of handling. The lifting handles may comprise rings encircling the body which also serve as roller chimes.
Various method have been utilized to attach lifting surfaces or handles to thermoplastic blow-molded hollow bodies. For large bodies such as drums, it is known to place prefabricated roller hoops into a blow-mold so that the hoops are welded to the drum when the parison is inflated. Such construction has resulted in separation of the hoops from the drums during handling. In order to avoid such separation problems, some processes employ channels formed in the mold cavity into which a portion of the thermoplastic material of the parison is forced. The channels are defined by moveable components of the mold. After the plastic material has been forced into the channel, the moveable components compress the material into a desired shape of a chime or handle. The latter method is disclosed, for example, in U.S. Pat. Nos. 4,228,911 and 4,529,570. It is believed that a disadvantage of this type of construction is a weakened area at the point at which the chime joins the drum. Although it has been proposed to increase the volume of material and therefore the wall thickness in the area of the protrusion, such extra material also has a tendency to undesirably increase wall thickness over a broad area. Accordingly, the thickness and location of rings are limited in this type process. Furthermore, in order to minimize stress cracks, these compression molded rings are formed of very low melt index materials (approximately 2 HLMI) resulting in processing difficulties requiring non-conventional extrusion equipment.
An example of a process for welding or bonding roller chimes to a plastic drum is set forth in U.S. Pat. No. 3,960,474. In that patent, the pre-formed chimes or hoops are placed in a blow-mold and a parison inflated such that the soft thermoplastic material of the parison adheres to the preformed chimes. The bond between the chimes and drum thus depends on the ability of the plastic material to adhere to the chime material, and such bonds have been known to separate under stress, such as by lifting of a filled drum by the chime.